There are some arguments which are more challenging than others. The capital punishment argument is particularly unsatisfying because it is so easy to refute.

Right-wing blogger Guido Fawkes has managed to drag the issue into the silly-season spotlight via the government's new e-petition system, which guarantees a debate in the Commons if you can get 100,000 signatures.

I neither support capital punishment nor have much regard for the arguments of those who do, but this seems a healthy and rewarding endeavour. Most people in this country do support executions but it remains a non-issue in Westminster. It seems entirely right that the petition should get the requisite signatures and trigger a Commons debate. Quite where it would go from there, given our international treaty obligations and membership of the European Union, is pretty obvious: nowhere. The rash of Tory backbenchers who have lent their support, including Philip Davies, Priti Patel, Andrew Turner and David Nuttall, will do little to change that.

Guido's petition demands that "the Ministry of Justice… map out the necessary legislative steps which will be required to restore the death penalty for the murder of children and police officers when killed in the line of duty".

The decision to call for executions only in certain murder cases is page one, chapter one, of the gradualist political method, but it does not alter the fact that pro-death penalty arguments of any sort can be dismantled with one sentence: the death penalty does not reduce crime. By the time you demonstrate that, and it is readily demonstrable, you realise that demands for the death penalty say considerable more about the personality of people who make them than they do about criminal justice.

All the best research comes from the United States, a factwhich is not without relevance, because the US is the only developed, supposedly civilised country which still conducts executions. Well, apart from China, Iran, North Korea, Yemen, Saudi Arabia, Libya, Syria and the other charming company it keeps in the top-ten spot.
A quick look at the statistical evidence will tell you that the death penalty has no deterrent effect on crime.

From 1976 to 1996, the number of annual executions in the US increased from zero to just under 60, but the homicide rate remained constant. A 1967 study by Thorsten Sellin compared homicide rates between neighbouring states - one with the death penalty and the other without. There were no statistically valid differences. A 1998 research study by the United Nations concluded: "This research has failed to provide scientific proof that executions have a greater deterrent effect than life imprisonment. Such proof is unlikely to be forthcoming. The evidence as a whole still gives no positive support to the deterrent hypothesis."

The most influential voice for the deterrent argument was University of Buffalo Professor Isaac Eehrlich, whose article stressing that each execution saves "eight innocent lives" was widely quoted and replicated. Professor Eehrlich was a modest and cautious man and he was careful to caveat his findings and highlight the inherent weakness of his methodology in a way which capital punishment campaigners have traditionally ignored. His results were quickly torn apart by scientists leaving the National Academy of Sciences to roundly reject his conclusions in a 1978 report.

Modern social science rules mean most current-day researchers wouldn't even stop to laugh at this sort of study, which is still cited by advocates of capital punishment, sometimes even with a straight face. When comparing statistics of this sort, it's very hard to control for certain factors, but the studies which followed Eehrlich failed in the most spectacular ways possible. Most did not take into account incarceration rates or life sentences, both factors which have a much stronger causal link with deterring crime, if only because the criminal is unable to commit the crime while in jail. Most studies did not factor in other variables, such as drug epidemics. Many of them did not differentiate between different types of murder, even though research strongly suggests that domestic murders (the husband who loses it after coming home to find his wife with another man etc) are much less likely to be affected by potential criminal sanctions than pre-meditated killings.

In actual fact, much of the data suggests capital punishment might actually encourage murder. In 1996, those US states with the death penalty had an average murder rate of 7.1 per 100,000 of population. Those states without had 3.6 per 100,000. In the same year, a Bureau of Justice Statistics report showed that southern US states, where 81% of executions were performed, had an average murder rate of nine per 100,000. Northeast states, which account for one per cent of executions, had a rate of 5.4.

A 1980 study in New York found that the month after an execution the average number of murders in the state rose. Fifteen years later another study in California showed similar results, with murders increasing by ten per cent when the state was still executing prisoners (from 1952 to 1967). When it stopped executing people (from 1968 to 1991) the rate of increase dropped significantly to 4.8%.

Again, this sort of data set has so many variables you should be cautious of coming to firm conclusions, but it's not so fanciful to posit that the acceptance of killing by the state has a moderate normalising effect on the rest of society.

Once the deterrent argument falls apart, capital punishment proponents have very little to fall back on but their own sense of emotional outrage, which is an unsuitable basis for political debate. Of course, victims of crime deserve to see their perpetrator punished, but that is a side-effect of deterrence and rehabilitation – not a guiding principle.

We should be more sympathetic, however, to proponents like David Nuttall who callg for a return to executions on the basis of certain crimes (in his case, murder) than those like Guido, who want a return on the basis of certain victims. The aim is obvious: to use the most emotional murders (children and on-duty policemen) to get the thin end of the wedge in with an eye to later expanding the punishment for all murders. But the consequence of dividing murder victims is the suggestion that some murders are more tolerable than others.

Even if we did want to divide victims into groups I certainly wouldn’t put police in the upper category with children. Given that the policeman knows the dangers of his job and does it anyway, surely that, if anything, suggests the murder is less horrific than if it is in the case of unsuspecting member of the public. It’s a weird, horrible thing to juggle, which is why you shouldn't propose it in the first place, but if you are going to play that game Guido's conclusion does not seem to morally follow.

So, a quick summary, just in case someone offers you an e-petition to sign. This policy would force us to derogate from the European Convention on Human Rights, drop out the European Union and recognise a distinction between types of victim in the criminal justice system. It would not stop any crime, although it might arguably encourage them. It also happens to be considerably more expensive than penal sanction (£1.5 to 3 million per execution compared to £600,000 for a life sentence).

Or, if you prefer it, the short version: it doesn't work.

The opinions in politics.co.uk's Comment and Analysis section are those of the author and are no reflection of the views of the website or its owners.